Constant torque drive means for typewriter



April 11, 1967 w. o. CRALLE, JR 3,313,389

CONSTANT TORQUE DRIVE MEANS FOR TYPEWRITER Filed Sept. 25, 1963 I I I Q I i I I I I I I I I I I I FIG.1

INVENTOR WALTER 0. CRALLE,JR.

ATTORNEY.

United States Patent Ofiiice Patented Apr. 11, 1967 3,313,389 CONSTANT TORQUE DRIVE MEANS FOR TYPEWRETER Walter 0. Cralle, Jr., Lexington, Ky assignor to International Business Machines Corporation, New York,

N.Y., a corporation of New York Filed Sept. 25, 1963, Ser. N 311,376 11 Claims. (Cl. 197-82) The present invention relates generally to the typewriter and printing arts and more particularly to the provision of a mechanism for maintaining a substantially constant torque on a lead screw which serves to control the movement of a typewriter carrier in either longitudinal direction.

In a co-pending application Ser. No. 311,373, entitled Proportional Escapement Apparatus for a Single Element Typewriter, filed September 25, 1963, concurrently with this application and which is assigned to the assignee of the present invention, there is shown and disclosed a typewriter having highly improved proportional escapement control apparatus. The proportional escapement control apparatus comprises a pin wheel mounting a plurality of pins, each of which is movable to a set or reset state. A pin setting assembly determines the states of the pins in accordance with the characters selected by the typist. An escapement pawl assembly is responsive to the set pins and limits the rotation of the pin wheel during each escapement operation. The pin wheel is drivingly connected with a lead screw which moves the typewriter carrier in a forward spacing or backspacing direction depending on the direction of rotation of the pin wheel and lead screw. In a cycle of operation of a typewriter only a certain amount of time is available in which an escapement movement can take place and it is necessary that the escapement movement occur within the predetermined time interval regardless of the position of the typewriter carrier along a typing line.

Briefly, the present invention relates to a mechanism for maintaining a substantially constant torque on a driven member which can be rotated in either direction, such as a lead screw in a typewriter that moves a typewriter carrier. The mechanism comprises a spiral spring acting to turn the lead screw and advance the typewriter carrier. An input member is caused to intermittently oscillate and during movement of the input member in one direction the spiral spring is Wound via a clutch spring. When the input member moves in the other direction, a second clutch spring prevents unwinding of the spiral spring. Means are provided for selectively disengaging the clutch springs whenever the spiral spring is wound to a predetermined extent either in response to movement of the input member in the one direction or rotation of the lead screw to backspace the typewriter carrier.

It is the primary or ultimate object of the invention to provide a mechanism for maintaining a constant torque on an intermittently driven member, such as a lead screw in a typewriter. A spiral spring is wound to a predetermined extent prior to each intermittent movement of the driven member in one direction so that the time required for a unit movement of the driven member remains substantially constant during each intermittent movement.

Another object of the invention is to provide a constant torque device for maintaining a substantially constant torque on a driven member regardless of the direction of movement of the driven member. Clutch means prevent the spiral spring from being wound beyond a predetermined extent even when the driven member moves in a direction that applies forces to the constant torque device tending to wind the spiral spring.

A further object of the invention is the provision of a constant torque device having the characteristics above described which is highly simplified in construction and operation and can be manufactured at a relatively low cost. The constant torque device is adapted to operate over long periods of time in a reliable manner with a minimum of maintenance and adjustment.

The foregoing and other objects and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings.

In the drawings:

FIGURE 1 is a perspective view of a constant torque device used in a typewriter and constructed in accordance with the teachings of the invention; and

FIGURE 2 is an end sectional view taken along the section line 22 of FIGURE 1.

Referring now to the drawings, the reference number 1 designates an interchangeable print element which is detachably secured to a mounting post 2. The print element 1 is mounted from a rocker plate 3 which in turn is pivoted by pins 4 to a carrier 5. The carrier 5 is mounted for longitudinal sliding movement on a print shaft 6 by a print sleeve 7 carrying a print cam 8. The print sleeve 7 is slidable along and rotatable with the print shaft 6 so that when the print shaft 6 rotates, the print cam 8 pivots the rocker plate 3 about pins 4 to throw the print element 1 toward an elongated and stationary printing platen 11').

The print element 1 has the shape of a truncated spheroid and a plurality of characters of different widths are formed in generally aligned vertical and horizontal rows thereon. The typewriter is provided with a plurality of character keylevers, not shown, and a number of function keylevers, also not shown, including a case shift keylever. Each of the character keylevers is associated with two of the characters formed on the print element and is operative to actuate character selection apparatus, not shown, for rotating and tilting the print element to bring one of the characters into printing position as determined by the state of the case shift keylever. This character selection apparatus and the mechanisms for rotating and tilting the print element 1 may be of the type employed in the single element typewriter marketed by International Business Machines Corporation under the trademark Selectric.

The carrier 5 has a driving connection with an elongated lead screw 12 which extends in generally parallel relation with respect to the printing platen 10. The lead screw 12 is rotated by means to be hereinafter more fully described to move the carrier 5 and the print element 1 in either longitudinal direction to various printing positions in front of the printing platen 10. The directions of rotations and angular distances moved by the lead screw determine the extent of forward escapement movements and the extent of backspacing movements of the print element 1 and the carrier 5.

Mounted on one end of the lead screw 12 is a pinion gear 14 whose teeth mesh with gear teeth formed about the outer periphery of an annular spring housing 15. The spring housing 15 is rotatably mounted on an elongated sleeve 16 which in turn is received over and I0- tatable with respect to an input shaft 17. The input shaft 17 is supported by a side plate 18 of the typewriter which also supports one end of the elongated lead screw 12. The input shaft 17 and the lead screw 12 extend in parallel relation.

The spring housing 15 is generally cup-shaped and has an outwardly extending integral circular flange 19 which, in combination with the sleeve 16, defines an annular recess for receiving a spiral spring 20. The inner end of the spiral spring it attached to the elongated sleeve 16 while :3 the outer end of this spring is connected to spring housing 15. The spiral spring 20 is wound in such a manner that the spring housing 15 is biased for counterclockwise rotation with respect to sleeve 16 and, as a consequence, the lead screw 12 is adapted to be rotated clockwise to control movement of the carrier 5 and print element 1 from left to right in front of the printing platen as shown in FIGURE 1 of the drawings.

Mounted on the outer end of the input shaft 17 in coaxial and longitudinally spaced relation with respect to elongated sleeve 16 is a sleeve 22. This sleeve is rigidly attached to the input shaft 17 by a set screw and is rotatable therewith. Received in overlying and spanning relation with respect to the sleeves 16 and 22 is a clutch spring 23. The clutch spring 23 is right hand wound and has one end thereof attached to the sleeve 16 while the other end provides a radially extending projection 24. An annular cover plate 25 covers the open end of spring housing 15 and has an outwardly extending clutch release arm 26 which, at certain times, is adapted to engage the projection 24 of clutch spring 23.

The inner end of the input shaft is rotatably supported in an elongated annular collar 28 formed in the side plate 18. Received in overlying relation and spanning the collar 28 and the elongated sleeve 16 is a left hand wound clutch spring 29 whose outer end is attached to the sleeve 16. The other end of the clutch spring 29 defines a projection 30 which is adapted to be engaged by a clutch release arm 31 carried by and movable with the spring housing 15.

A lever 32 is carried on the inner end of the input shaft 17 and is connected by link 33 to one arm of a bellcrank 34. The other arm of the bellcrank 34 carries a cam follower roll 35 which is biased against a cam 36 rotatable with the print shaft 6 by tension spring 37. The arrangement is such that the input shaft 17 oscillates each time the print shaft 6 is rotated to effect a printing operation.

The right end of the lead screw 12 is connected by suitable gearing means, represented 'by pinion gears 38 and 39, to an escapement pin wheel 40 having a plurality of equally spaced pins 41 about the outer periphery thereof. The pins 41 are adapted to be engaged by the tip of an escapement pawl 42 having an elongated slot 43 therein which serves to mount the escapement pawl 42 for pivotal and longitudinal movement on pin 44. A spring 45 biases the escapement pawl forwardly and downwardly into engagement with the pins 41 on the escapement pin wheel 40. An escapement pawl release lever 46 is also pivoted on the pivot pin 44 and has a transversely extending tab 47 which overlies the rear end of the escapement pawl 42. counterclockwise movement of the escapement pawl release lever 46 causes the tab 47 thereof to engage and pivot escapement pawl 42 so the tip is removed from engagement with the pins 41. The lead screw 12 and escapement pin wheel 40 are now free to rotate under the action of the constant torque drive means including the spiral spring 20. The spring 45 immediately moves the escapement pawl 42 forward until the rear edge of elongated slot 43 abuts against the pin 44. The tip of the escapement pawl then is pivoted downwardly into the path of travel of the pins 41 and is engaged by the next adjacent pin. The escapement pawl 42 is moved back to the position shown in FIGURE 1 of the drawing and the apparatus is again ready for another escapement operation. During the escapment operation, the carrier 5 and print element 1 have moved under the action of spiral spring 20 to a new printing position.

For actuating the escapement pawl trip lever 46 at the end of each printing operation, a link 50 extends to a bellcrank 51 mounting a cam follower roll which engages escapement cam 52. The escapement cam 52 rotates with the print shaft 6. It should be noted that each time the print shaft 6 is rotated, the cams 8, 36 and 52 mounted thereon actuate several operations in a desired sequence.

The print element 1 is thrown toward the printing platen 10 by cam 8, the input shaft 17 is oscillated by cam 36 and the escapement pawl 42 is released by cam 52.

In typing it is often desired to backspace or move the carrier 5 and print element 1 from right to left in front of the printing platen 10 to previous printing positions. For this purpose, a backspace pawl 55 is pivoted on a lever 56 which is journalled on the shaft mounting the escapement pin wheel 40. An end portion of the backspace pawl 55 engages a fixed stop 57. An arm 58 of the lever 56 has a link attached thereto which extends to suitable typist actuated backspace drive apparatus, not shown. A pulling force on link 59 rotates lever 58 clockwise and the backspace pawl 55 is moved upwardly from the stop 57. A spring 60 immediately pulls escapement pawl 55 into engagement with the pins 41 and the escapement pin wheel is rotated in the backspace direction. The lead screw 12 rotates in a counterclockwise direction and the print element 1 and carrier 5 move to a previous printing position.

The above described escapement and backspace assemblies should be considered only as schematic and representative disclosures of escapement control apparatus capable of limiting the rotation of the lead screw 12 in one direction against the action of spiral spring 20 and backspacing apparatus capable of rotating the lead screw in the opposite direction. For example, a backspace holding pawl would usually be provided to accurately hold the pin wheel during backspacing operations. Also, the pins 41 can be movable elements settable to either of two states in accordance with the size or width of the character selected by the typist. For those desiring a more detailed description of preferred forms of the escapement control apparatus and backspacing apparatus, reference should be made to the above-identified application entitled Proportional Escapement Apparatus for a Single Element Typewriter.

Considering now the operation of the constant torque drive means of the invention, the print shaft6 is rotated and cam 36 causes oscillation of the lever 32. When input shaft 17 rotates in a counterclockwise direction, the right hand wound clutch spring 23 provides a driving connection between the sleeves 22 and 16 to cause a winding and tensioning of the spiral spring 20. The spring housing 15 cannot rotate at this time since the escapement pawl 42 engages one of the pins 41 and holds the escapement pin wheel 40. Also, the left hand wound clutch spring 29 slips to permit counterclockwise movement of the sleeve 16 and input shaft with respect to the collar 28. The spiral spring 20 is wound to a predetermined extent at which time the projection 24 of the clutch spring 23 engages clutch release arm 26. This releases the clutch spring 23 and breaks the driving connection between the input shaft 17 and the sleeve 16. The input shaft 17 can still rotate in the counterclockwise direction but the spiral spring 20 is not further wound after the projection 24 engages clutch release arm 26. Unwinding of the spiral spring 20 is prevented by clutch spring 29 which engages and holds the sleeve 16 to stationary collar 28 whenever a clockwise rotating force is applied to sleeve 16.

The continued rotation of the cam 36 eventually causes the input shaft 17 to change its direction of rotation. Clockwise rotation of the input shaft has no effect on the previously wound spiral spring 20 since right hand clutch spring 23 is not engaged under this condition. The clutch spring 29 prevents unwinding of the spiral spring 20. It should be apparent that the clutch springs 23 and 29 permit only uni-directional movement of the sleeve 16 to wind the spiral spring 20 to a predetermined extent in response to oscillating rotation of the input shaft 17. Also, once the spiral spring 20 has been wound to a predetermined extent, the clutch spring 23 is released to prevent further winding of this spiral spring.

During a backspacing operation, the lead screw 12 is driven in the opposite direction by the escapement and backspace apparatus. The spring housing 15 is rotated in a counterclockwise direction by pinion 14 and, since sleeve 16 is held stationary by clutch spring 29 at this time, the outer convolutions of the spiral spring 20 are moved in a direction to wind the spiral spring. When the spiral spring 20 has been wound to a predetermined extent, the clutch release arm 31 engages projection 30 of clutch spring 29 to disengage the same. The spring housing 15, spring 26 and sleeve 16 then rotate as a unit during the remainder of the backspacing operation and the spiral spring is not further wound.

It should now be apparent that the objects initially set forth have been accomplished. A drive means for maintaining a substantially constant torque on a lead screw in a typewriter has been provided. Of course, the spiral spring is selected to provide a relatively constant torque over the largest escapement movement expected. Also, the predetermined point to which the spring is Wound either by rotation of the input shaft or the lead screw is selected to provide a torque which will move the carrier and print element through the largest escapement distance within the time interval of an operating cycle alloted for escapement operations. The system is so designed that the total movements of the input shaft and the lead screw in the backspace direction are greater than the driving movements imparted to the lead screw by the constant torque drive means. In this manner, the spiral spring always maintains a substantially constant torque on the lead screw.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A constant torque device for maintaining a substantially constant torque on a lead screw used in a typewriter to control movement of a typewriter carrier wherein the lead screw is driven by said constant torque device in one direction and said lead screw drives said constant torque device when said lead screw is rotated in the opposite direction comprising:

an input shaft and means to oscillate said input shaft;

a sleeve member received over said input shaft and rotatable independently thereof;

an annular spring housing received over said sleeve and rotatable independently thereof;

driving means interconnecting said spring housing and the lead screw of the typewriter to permit rotation of said lead screw in one direction by said spring housing and driving of the spring housing by said lead screw when said lead screw is rotated in the opposite direction;

a spiral spring received in said spring housing and having one end connected to said sleeve and the other end connected to said spring housing;

a first clutch spring interconnecting said input shaft and said sleeve to permit winding of said spiral spring when said input shaft rotates in one direction and to permit relative movement between said sleeve and said input shaft when said input shaft rotates in the other direction;

a stationary member and a second clutch spring interconnecting said sleeve and said stationary member; and

said second clutch spring being wound in a direction opposite to the direction in which said first clutch spring is wound to hold said sleeve against rotation when said input shaft rotates in said other direction and to permit winding of said spiral spring when said lead screw is rotated in said opposite direction to drive said annular spring housing.

2. Apparatus according to claim 1 further characterized said typwriter comprising a single print element mounted on said carrier;

5 a print shaft mounting a print cam for moving said print element in a printing direction when said print shaft is rotated; and

said means to oscillate said input shaft comprising said print shaft.

3. Apparatus according to claim 1 further characterized'by:

clutch release means for each of said clutch springs; and

means to actuate one of said clutch release means in response to said spiral spring being wound to a predetermined extent from said input shaft and means to actuate the other of said clutch release means in response to said spiral spring being wound to a predetermined extent from said lead screw.

4. Apparatus according to claim 3 further characterized by:

said clutch release means comprising a projection ex tending from each of said clutch springs; and

said means to actuate comprising a pair of clutch release arms carried by said spring housing adapted to engage said projections.

5. A device for maintaining a substantially constant force on a driven member used in a typewriter to control movement of a typewriter carrier wherein the driven member is driven by said device in one direction and said driven member drives said device when said driven member moves in the opposite direction comprising:

an input member and means to oscillate said input member;

a housing member having a driving connection with said driven member to permit movement of said driven member in one direction by said housing member and driving of the housing member by said driven member when said driven member moves in the opposite direction;

an intermediate member mounted for movement independently of said housing member and said input member;

an energy storage device connected between said housing member and said intermediate member;

a first uni-directional clutch means interconnecting said input member and said intermediate member to couple said input member and said intermediate member to power said energy storage device when said input member moves in one direction; and

stationary member and a second uni-directional clutch means interconnecting said intermediate memher and said stationary member to couple said intermediate member to said stationary member when said intermediate member tends to move in a direction opposite to said one direction and to power said energy storage device when said driven member moves in said opposite direction to drive said housing member.

6. Apparatus according to claim 5 further character- 60 ized by:

clutch release means for each of said uni-directional clutch means; and

means to selectively and automatically actuate said clutch release means in response to a predetermined amount of energy being stored in said energy storage means.

7. Apparatus according to claim 6 further characterized by:

said first and second uni-directional clutch means each comprise a clutch spring having one end attached to said intermediate member; and

each of said clutch springs having a projection defining said clutch release means.

8. A device for maintaining a substantially constant force on a driven member wherein the driven member is driven by said device in one direction and said driven member drives said device when said driven member moves in the other direction comprising:

an input member and means to drive said input memher;

a housing having a driving connection with said driven member to permit movement of said driven member in one direction by said housing and driving of the housing by said driven member when said driven member moves in the opposite direction;

an intermediate member mounted for movement independently of said housing and said input member;

an energy storage device connected between said intermediate member and said housing;

a first uni-directional clutch means connecting said input member and said intermediate member to power said energy storage device when said input member moves in one direction; and

a stationary member and a second uni-directional clutch means interconnecting said stationary member and said intermediate member to power said energy storage device when said driven member moves in said opposite direction to drive said housing.

9. Apparatus according to claim 8 further characterized by:

said first and second uni-directional clutch means comprise a pair of clutch springs wound in the opposite direction with respect to each other.

10. A constant torque device for maintaining a substantially constant torque on a lead screw used in a typewriter to control movement of a typewriter carrier comprising:

an input shaft and means to rotate said input shaft;

a sleeve member received over said input shaft and rotatable independently thereof;

an annular spring housing received over said sleeve and rotatable independently thereof;

driving means interconnecting said spring housing and the lead screw of the typewriter;

a spiral spring received in said spring housing and having one end connected to said sleeve and the other end connected to said spring housing;

a clutch spring overlying and interconnecting said input shaft and said sleeve to permit winding of said spiral spring when said input shaft rotates in one direction;

a projection extending from said clutch spring; and

a clutch release arm carried by said housing and engageable with said projection to disengage said clutch sprin when said spiral spring has been wound to a predetermined extent.

11. A device for maintaining a substantially constant 0 force on a driven member wherein the driven member is driven by said device comprising:

an input member and means to drive said input memher;

a housing having a driving connection with said driven member;

an intermediate member mounted for movement independently of said housing and said input member;

an energy storage device connected between said intermediate member and said housing and received within said housing;

a uni-directional clutch means interconnecting said in put member and said intermediate member to permit the storing of energy in said energy storage device; and

clutch release means comprising an arm carried by said housing for disengaging said uni-directional clutch means when a predetermined amount of energy has been stored in said energy storage device.

References Cited by the Examiner UNITED STATES PATENTS 1,550,740 8/1925 Phelps 197-62 2,854,124 9/1958 Dodge et al. 197183 2,909,935 10/1959 Dodge 197-64 X 2,914,956 12/1959 Maclay 58-48 X 2,915,906 12/1959 Scott et al 58-48 X 3,135,371 6/1964 Young 19716 3,225,886 12/1965 Cetran et al. 19784 ROBERT E. PULFREY, Primary Examiner.

E. T. WRIGHT, Assistant Examiner. 

1. A CONSTANT TORQUE DEVICE FOR MAINTAINING A SUBSTANTIALLY CONSTANT TORQUE ON A LEAD SCREW USED IN A TYPEWRITER TO CONTROL MOVEMENT OF A TYPEWRITER CARRIER WHEREIN THE LEAD SCREW IS DRIVEN BY SAID CONSTANT TORQUE DEVICE IN ONE DIRECTION AND SAID LEAD SCREW DRIVES SAID CONSTANT TORQUE DEVICE WHEN SAID LEAD SCREW IS ROTATED IN THE OPPOSITE DIRECTION COMPRISING: AN INPUT SHAFT AND MEANS TO OSCILLATE SAID INPUT SHAFT; A SLEVE MEMBER RECEIVE OVER SAID INPT SHAFT AND ROTATABLE INDEPENDENTLY THEREOF; AN ANNULAR SPRING HOUSING RECEIVED OVER SAID SLEEVE AND ROTATABLE INDEPENDENTLY THEREOF; DRIVING MEANS INTERCONNECTING SAID SPRING HOUSING AND THE LEAD SCREW OF THE TYPEWRITER TO PERMIT ROTATION OF SAID LEAD SCREW IN ONE DIRECTION BY SAID SPRING HOUSING AND DRIVING OF THE SPRING HOUSING BY SAID LEAD SCREW WHEN SAID LEAD SCREW IS ROTATED IN THE OPPOSITE DIRECTION; A SPIRAL SPRING RECEIVED IN SAID SPRING HOUSING AND HAVING ONE END CONNECTED TO SAID SLEEVE AND THE OTHER END CONNECTED TO SAID SPRING HOUSING; A FIRST CLUTCH SPRING INTERCONNECTING SAID INPUT SHAFT AND SAID SLEEVE TO PERMIT WINDING OF SAID SPIRAL SPRING WHEN SAID INPUT SHAFT ROTATES IN ONE DIRECTION AND TO 